Slotless, brushless, large air-gap electric motors are well known and used in a variety of applications. These applications include use in power tools, consumer appliances, and the automotive industry to name but a few.
Due to the nature of this type of motor, for different applications, the motor must be substantially redesigned to provide the desired torque and horsepower. Additionally, a different electronics package ordinarily would be necessary to control each different motor. As a result of these factors and the difficulty of manufacturing slotless, brushless motors, the motors become a major cost factor for many of the items in which they are employed or in which it would be desirable to employ them. An example is in the power tools or appliances mentioned above. Consequently, reducing the cost of the motor in these and other appliances and applications would greatly impact the overall cost of the complete item. Moreover, in large, high volume applications for such motors, e.g., in the automobile industry, although the cost of one or even a few motors may not contribute significantly to the cost of an item, say an automobile, the overall motor cost as a result of volume would be significant and a reduction of that cost would be advantageous.
Slotless, brushless, large air-gap motors also are relatively inefficient. Some inefficiencies are due to hysteresis and eddy current losses as well as other losses that typically are dissipated as heat. Another exemplary inefficiency is the limitation on use with only one type of input electrical energy, namely either from a direct current or an alternating current power supply. Improving the efficiency of such motor and permitting its use with both types of power supplies interchangeably, would allow the motors to more readily be used in general and would expand the market for such motors. For instance, it would be desirable for such a motor to be used in an appliance, such as a hand drill, that would be able to run less hot than a conventional hand drill and that also either could be plugged into a wall outlet or alternatively could be powered by a battery pack.